1. Field of Invention
The present invention pertains to controllers of downhole tools used in subsurface well completions, and particularly to remotely actuated controllers.
2. Related Art
It is often desired to control downhole tools and equipment from the surface without using a dedicated communication medium, such as a wire, tube, or fiber optic cable. Whenever an existing medium such as drill pipe or wellbore fluids can be used, operating a downhole tool or device can be simplified and cost reduced.
Some prior art controllers that use such an existing medium use a set of predefined pressure sequences or expected pressure profiles programmed into a processor or other memory device to identify an actuation command sent from a remote location. The controller monitors pressure variations in the medium. Such variations may be monitored continuously or sampled discreetly. By comparing the received waveform with the reference pressure pulses, the controller is able to discriminate between noise and a command signal. When a command signal is detected, the controller responds by actuating a downhole device.
In wells with open perforations, it is sometimes difficult to send signals to a controller that uses predefined pressure sequences as a reference. To produce a response from the controller, the controller must receive pressure signals that match those pre-programmed pressure sequences within certain ranges of amplitudes and with changes at appropriate rates. Open perforations make it difficult or impossible to transmit and receive such sequences due to the wide variations in formation pressure, porosity, well fluids, and permeabilities normally encountered in a well.